1. Field of the Invention
The present invention relates to the clarification of liquids to remove suspended solids. Even more particularly, the present invention relates to the clarification of liquids to remove suspended solids using media and having continuous downward clarification as well as continuous media cleansing, wherein the influent stream is contacted by activated floc attached to floc carrier particles as influent and bed mix during cleansing of the bed.
2. General Background
Various devices are known which attempt to clarify a waste stream or turbid water stream prior to its consumption or use in a power plant, manufacturing facility, or other such industry or for municipal use in a potable water system.
Clarifiers are one such type of device used in an attempt to clarify turbid or waste water. These devices in a crude fashion date back to the time of the early Egyptians. In a clarifier a coagulation blanket is held in position by upward flow into the clarifier. This reduces the suspended solids content of the incoming stream. Problems arise in the use of clarifiers when the sludge blanket is lost. When the sludge blanket is lost there is little or no reduction in turbidity. This is compounded by the fact that particle mass increases since such turbid water is usually preflocculated by adding a polymer. The sludge blanket can be lost, for example, due to rapid flow changes, lost of PH control, convection, mechanical failure due to internal moving parts, and the introduction of very cold clean water into the clarifier with the inlet stream.
Once the sludge blanket is lost and with low water temperature and low suspended solids, there can be a very long recovery rate, up to days. Traditional clarifiers require a large area in which to operate and they tend to add dissolved solids to the water and alter the natural PH of the water. The sludge produced from such clarifiers is difficult to de-water.
Another type of conventional water treatment is the use of sand filters. Sand filters are a down flow type filter which can be effective in treating water provided the influent is at a very low suspended solids level. Significant disadvantages accompany the use of sand filters. Generally such sand filters are a batch process which must be stopped and cleaned periodically. The pressure needed to flow a stream through the unit increases with time due to the continuous buildup of solids in the sand bed. Clean water is required for proper cleansing which is usually accomplished by back flushing. The use of a sand filter is very susceptible to the formation of mud balls which can incapacitate the sand filter unit. Sand filters generally have poor polyelectrolyte efficiency as many "sites" (i.e., places where solid material could attach) are never used and are discarded during cleansing or flushing. Such a unit often channels due to mixing of the media (when multiple medias are required). High intermittent flush volumes are required and high intermittent air volumes are required in the cleaning procedure. Such high volumes raise energy requirements and operating costs.
Sand filters are generally restricted to a very limited capacity for the treatment of suspended solids such as, for example, an influent maximum of twenty to thirty parts per million.
Upflow type sand filters have the same disadvantages generally as the downflow type sand filter with the exception possibly of the need for clean water in order to effect proper cleansing and the electrolyte efficiency is somewhat greater than sand filters of the downflow type.
A tight compacted media bed is necessary for the effective filtration of turbid fluids. Such a tight compacted media bed is accomplished in many cases by utilizing a downflow direction. Effective media cleaning is accomplished by simultaneous aeration and flushing in an upward direction at such a rate as to fluidize the media uniformly. A desirable feature is to flush with unclarified water at a minimum flush rate.
U.S. Pat. No. 4,126,546 issued to Hjelmner, et al, provides an upflow type continuous filter method.
U.S. Pat. No. 2,057,887 shows a clarifying liquid apparatus.
In U.S. Pat. No. 3,395,099 issued to R. D. Johnson there is seen a method and means for backwashing mineral beds.
In U.S. Pat. No. 3,537,582 a liquid filter container utilizing sand is shown.
In U.S. Pat. No. 3,581,895 there is seen an automatic backwashing filter system for swimming pools.
Movement bed apparatus for the treatment of fluid is the subject of U.S. Pat. No. 3,667,604.
A method and apparatus for ultrasonically clarifying liquid is seen in U.S. Pat. No. 3,707,230.
An automatically backwashed gravity filter is the subject of U.S. Pat. No. 3,841,485.
Many of these devices suffer in that they provide for the backwashing of the filter bed rather than a continuous cleansing and filtration. Other such devices which attempt to provide continuous cleansing and filtration, suffer in that the continuous filtration is either ineffective, or the apparatus is unworkable when flow-flux rate increases.
Some patented devices are upflow type which can lose efficiency during cold water temperature periods when viscosity increases thus enhancing the chance for fluidization of the bed.
Other devices use only a small portion of the flow value through the unit to cleanse the dirtiest portion of the filtrate media or sand or the like.